To address the clinical concerns of immunogenicity and suboptimal pharmacokinetics, cancer therapy with monoclonal antibodies has evolved from murine to chimeric, humanized, and fully human constructs. Parallel to these improvements have been continuing efforts to develop more effective forms of antibodies, which to date include different antibody isotypes, single-chain antibody fragments with monomeric or multimeric binding moieties, specific mutations in the Fc region to modulate effector function or circulating half-life, and bispecific antibodies of numerous designs that vary in valency, structure, and constituents (Chames et al., Br J Pharmacol 2009, 157:220-233).
Because signaling pathway redundancies can result in lack of response to a single antibody, diverse strategies to use combination therapy with antibodies that bind to different epitopes or different antigens on the same target cell have been proposed. Combinations such as anti-CD20 and anti-CD22 (Stein et al., Clin Cancer Res 2004, 10:2868-2878), anti-CD20 and anti-HLA-DR (Tobin et al., Leuk Lymphoma 2007, 48:944-956), anti-CD20 and anti-TRAIL-R1 (Maddipatla et al., Clin Cancer Res 2007, 13:4556-4564), anti-IGF-1R and anti-EGFR (Goetsche et al., Int J Cancer 2005, 113:316-328), anti-IGF-1R and anti-VEGF (Shang et al., Mol Cancer Ther 2008, 7:2599-2608), or trastuzumab and pertuzumab that target different regions of human EGFR2 (Nahta et al., Cancer Res 2004, 64:2343-2346) have been evaluated preclinically, showing enhanced or synergistic antitumor activity in vitro and in vivo.
The first clinical evidence of an apparent advantage of combining two antibodies against different cancer cell antigens involved the administration of rituximab (chimeric anti-CD20) and epratuzumab (humanized anti-CD22 antibody) in patients with non-Hodgkin lymphoma (NHL). The combination was found to enhance anti-lymphoma efficacy without a commensurate increase in toxicity, based on 3 independent clinical trials (Leonard et al., J Clin Oncol 2005, 23:5044-5051; Strauss et al., J Clin Oncol 2006, 24:3880-86; Leonard and Goldenberg, Oncogene 2007, 26:3704-13). Although these results are promising, a need exists in the field for more effective antibody-based combination therapies.